Conventionally, thermoplastic resins such as high density polyethylene, low density polyethylene, linear low density polyethylene and polyvinyl chloride have been employed as a material for blow molding in order to produce bottles or the like. Recently, so-called engineering plastics excellent in thermal properties and mechanical properties have been employed for electric and electronic appliances such as an air duct and lighting equipments, automotive parts such as an air spoiler and a console, furniture parts such as a top panel of a desk, and the like (e.g. Patent Document 1).
The above-mentioned blow molded articles of the engineering plastics and the like have a large number of small recessed parts (hereinafter, referred to as recesses) on the surfaces formed during the blow molding and, for example, an air spoiler for which a smooth coating surface is required, secondary processability by sanding has often been needed before coating. In this connection, it is supposed that the above-mentioned recesses are generated in a manner that a gas which is not completely extracted from the parting face of a mold and left between a parison made of a melted engineering plastic and the mold surface during the blow molding is left in form of a large number of small spheres on the molded article surface and thereafter, the engineering plastic is cooled and solidified.
On the other hand, ABS resin compositions for blow molding having resistance to formation of recesses on the surface of a blow molded article and excellent in impact resistance, heat resistance, rigidity, and blow moldability by blending specified amounts of specified graft copolymers and copolymers have been proposed (e.g. Patent Document 2).
However, even if products such as an air spoiler for which a smooth coating surface is required are produced using any of the above-mentioned materials for blow molding, polished powder of the molded article generated in a sanding process before coating adheres to the molded article surfaces or, for example, airborne dust adheres to the product surfaces during storage until the coating process, so that a work for removing them has to be carried out before the coating and the productivity may be lowered in some cases.
Further, the above-mentioned materials for blow molding all have high adhesion of the resin to a metal and therefore, at the time of forming a parison by extruding melted resin out of a die at the time of blow molding, the melted resin adheres to the metal surface of the die or the like to make smooth molding impossible or the adhered resin causes decomposition or thermal deterioration and becomes foreign matters to thereby blemish the surface appearance of the blow molded articles in some cases.
Furthermore, since a resin tends to adhere to the metal surface such as a screw surface, a barrel inner wall, or the like of a blow molding apparatus, an extruder, or the like, it sometimes becomes impossible to efficiently carry out purging of the resin or the replacement work for the resin.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 7-32454
Patent Document 2: JP-A No. 2001-214026